JPH10287418A - Production of synthetic quartz powder containing aluminum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a good synthetic quartz powder containing aluminum hardly foaming when melted. SOLUTION: This method for producing a synthetic quartz powder containing aluminum by adding an aluminum compound to a silicon alkoxide, adding water thereto to hydrolyze the silicon alkoxide with added aluminum compound and to form a gel, and further pulverizing, drying and firing the obtained gel comprises using a chelate compound of aluminum (preferably aluminum acetylacetonate) as the aluminum compound, allowing the mixture after adding the aluminum chelate compound to the silicon alkoxide to stand for >=5 hr, and thereafter adding water to start the hydrolysis reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the synthesis of quartz glass for semiconductors used in a high temperature region of 1000 ° C. or more, particularly for the semiconductor field, or for optics having a process which is subjected to a high temperature treatment when manufacturing optical fibers and the like. It relates to quartz powder and quartz glass products. In recent years, quartz glass products used in the semiconductor industry have been very strictly controlled with respect to their purity. In order to obtain such high-purity glass, it was conventionally produced by refining natural quartz and melting natural quartz powder obtained by grinding.
As the demand for higher integration and higher yield of semiconductors becomes more stringent, higher cost purification technology is required. On the other hand, as another method for obtaining high-purity quartz glass, there is a method using a gas phase method using silicon tetrachloride as a raw material, but it has a disadvantage that it requires a lot of energy and is inefficient. As a method for solving these problems, for example, a synthetic quartz powder is formed by a so-called sol-gel method by using an organosilicon compound such as silicon alkoxide as a raw material to form silica gel by a liquid phase reaction, and further drying, pulverizing, and firing to obtain glass. Get
There is a method in which this is melt-molded into a quartz glass product.
Since the sol-gel method is a liquid phase reaction, it can be produced with low energy and high efficiency. In addition, by using a sufficiently purified raw material, it is possible to obtain quartz glass having a certain degree of purity.

However, quartz glass products obtained by melt-molding synthetic quartz powder obtained by the sol-gel method have a lower high-temperature viscosity than those made from natural quartz powder, so that they can be used alone for high-temperature applications. There are few examples. For example, a double-structure crucible using natural quartz on the outside and synthetic quartz on the inside has been manufactured to ensure high-temperature strength.
40989). As a technique for improving the high-temperature viscosity of synthetic quartz glass itself, a method of adding a small amount of aluminum to glass is known (Japanese Patent Application Laid-Open No. 61-2 / 1986).
36619, JP-A-3-45530). The details of the mechanism of improving the high-temperature viscosity by adding aluminum have not been elucidated yet, but (1) ions such as Na, K, and OH which exist as glass-modified oxides (terminal groups) and lower the high-temperature viscosity. (2)
The prevailing theory is that high-melting alumina inhibits viscous flow of glass.

[0003]

It is considered that the addition of aluminum is preferably carried out at the time of hydrolysis in order to uniformly disperse it at the molecular level in glass. In fact, in the above-mentioned known techniques, aluminum alkoxide is added. Is added to the hydrolyzed solution of silicon alkoxide. However, alkoxides of aluminum and silicon have a remarkable difference in the rate of hydrolysis (aluminum alkoxide is much faster), and its handling, reaction conditions, and the like require great care. In order to simultaneously hydrolyze two or more alkoxides and uniformly disperse them, it is considered preferable to make the difference in the hydrolysis rate as close as possible.
As the aluminum source, a chelate compound, particularly aluminum acetylacetonate, is considered to have the highest hydrolysis stability and can be suitably used. In fact, the present inventors carried out a hydrolysis reaction in a system in which aluminum acetylacetonate was dissolved in tetramethoxysilane at a concentration of 5 ppm of Al in terms of SiO ₂ , and gelation, pulverization, drying and classification resulted in a particle size of 100 to 500 μm A silica gel powder having a distribution was obtained, which was made nonporous by heating and vitrified to obtain an aluminum-containing synthetic quartz powder. However, in the obtained aluminum-containing synthetic quartz powder, aluminum is
The present inventors confirmed that the doping was substantially performed with the charged composition, but blackened particles were observed in a part of the aluminum-containing synthetic quartz powder, and the particles were melted by an oxyhydrogen flame (Bernui method). However, there was a problem that many bubbles were present in the finished ingot.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that after adding a chelating compound of aluminum to silicon alkoxide, the hydrolysis reaction is immediately carried out for 5 hours or more, preferably 10 hours or more, without a hydrolysis reaction. By starting the hydrolysis reaction after standing, no black foreign matter is generated in the finally obtained synthetic quartz powder, and a transparent quartz glass body without foaming when this is melt-molded can be manufactured. The present inventors have arrived at the present invention. That is, the present invention is to add an aluminum compound to silicon alkoxide, then add water to hydrolyze, gel,
In producing aluminum-containing synthetic quartz powder by pulverization, drying, and firing, an aluminum chelate compound is used as an aluminum compound. After the aluminum chelate compound is added to the silicon alkoxide, the mixture is left for at least 5 hours, and then water is added. And initiating a hydrolysis reaction to produce a synthetic quartz powder containing aluminum.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As silicon alkoxide used as a raw material,
Although not particularly limited, it is preferable that all of the groups bonded to silicon are hydrolyzable groups from the viewpoint that carbon remaining in the obtained synthetic quartz powder can be easily prevented, and in particular, chlorine and the like are preferable. Tetraalkoxysilanes are particularly preferred in that they can also prevent the remaining of the compounds. Particularly, tetramethoxysilane is desirable from the viewpoint of low cost.

The present invention is characterized in that a chelate compound of aluminum is used as an aluminum source. It is not particularly limited as long as it is a chelate compound of aluminum,
For example, aluminum tris (ethylacetonate), aluminum monoacetylacetonate bis (ethylacetoacetate), and aluminum tris (acetylacetonate) (also referred to as aluminum acetylacetonate) can be given. Among them, aluminum acetylacetonate is particularly preferably used because of its close hydrolysis rate and high compatibility with silicon alkoxide. This aluminum chelate compound is added to the silicon alkoxide so as to have the above concentration in the final glass product. However, since the target concentration is low, the Al concentration is 60 to 1500 ppm, preferably 8 ppm, based on SiO _{2 in} advance.
It is more efficient and more efficient to adjust the concentration of Al by adjusting a concentrated solution of about 0 to 1200 ppm, leaving it to stand as described later, and then adding and using silicon alkoxide.

The amount of aluminum added for improving the high-temperature viscosity of the final glass product is sufficient if it is about 1 to 50 ppm based on SiO ₂ , and the effect of improving the high-temperature viscosity hardly changes even if it is added more. ,Also,
It is not preferable that the concentration of aluminum, which is an impurity for the semiconductor, becomes too high. On the other hand, if the added amount of aluminum is less than the above range, the effect of improving the viscosity that can sufficiently withstand use at a high temperature of 1000 ° C. or higher cannot be expected.

When the hydrolysis reaction is started immediately after the addition of the aluminum chelate compound to the silicon alkoxide, the dried gel obtained after gelling, pulverizing and drying reacts only with ordinary tetraalkoxysilane. The present inventors have found that the specific surface area is smaller than that of the gel obtained in the above, black foreign matter derived from unburned carbon is generated during firing, and foaming is increased when the gel is melted. . In order to avoid this, in the present invention, a silicon alkoxide to which an aluminum compound is added is left for 5 hours or more, preferably 10 hours or more, as described below.

At the time of standing, mixing, stirring, heating, etc. may be performed instead of simply standing, but generally the solubility of the aluminum chelate compound in the silicon alkoxide is large, and the aluminum chelate compound dissolves promptly when added, and is simply left standing after the addition. Then, the effect of the present invention is sufficient. In other words, it is not clear what mechanism is used, but surprisingly, by satisfying the simple requirement of not adding water required for hydrolysis for 5 hours or more after the addition, it is possible to suppress the generation of black foreign matter in the obtained quartz powder. This suppresses the generation of bubbles in the molded product obtained by melting the same.

Thus, when the Al concentration based on SiO ₂ in the silicon alkoxide left for a specific time exceeds the target concentration of the final glass product, the final Al to SiO ₂ concentration, preferably 1 to 1, The Al concentration is diluted by adding silicon alkoxide to 50 ppm, and then water is added to start the hydrolysis reaction. After the dilution with the silicon alkoxide, the effect of the present invention is not hindered even if the hydrolysis reaction is started immediately. The amount of water to be added is usually 1 equivalent to 10 equivalents required for the reaction. Further, an organic solvent such as alcohols, ethers, and ketones compatible with both the alkoxide and water may be mixed as needed during the hydrolysis. Examples of the alcohol include methanol, ethanol, and propanol, ethers include diethyl ether, and ketones include acetone.

However, since the alkoxy group bonded to the alkoxide is liberated as alcohol as the hydrolysis reaction proceeds, if the reaction solution becomes uniform before gelation, that is, the alkoxy group having a high hydrolysis rate In the case of a raw material having a methoxy group (for example, a methoxy group), the operation can be practically performed without adding an alcohol. It should be noted that all of these raw material liquids are of high purity.

[0012] The hydrolysis reaction is substantially completed after the formation of a homogeneous solution of the alkoxide and water. Next, after a homogeneous phase is formed, the solution may be allowed to stand until the solution gels. The conditions of the hydrolysis reaction and the gelation vary depending on the raw materials used, but are usually about 20 minutes to 10 hours under a normal pressure at a temperature of 20 to 80 ° C. In order to gel the hydrolyzate, a gel can be obtained immediately by heating, but it gels in a few hours even if left at room temperature,
By adjusting the heating temperature, the gelation time can be adjusted. The gel thus obtained is a wet gel containing usually 70% by weight or more of water.

The obtained wet gel is adjusted to an arbitrary particle size by pulverization. At this time, in order to obtain the target particle size distribution of the final product, the optimum particle size of the wet gel may be determined in consideration of the shrinkage due to drying and baking. Usually, the final product is adjusted to a particle size in the range of 50 to 1000 μm.

The pulverized wet gel is dried and calcined to obtain a synthetic quartz powder. Here, drying is usually 50 to
It is carried out at a temperature of 200 ° C. to remove free water and free methanol in the wet gel to obtain a dry gel. The obtained dry gel is finally made nonporous at a temperature of 1000 to 1300 ° C. Here, the carbon components (mostly alkoxy groups) remaining in the dry gel are sufficiently removed before the gel becomes nonporous, thereby suppressing foaming during melting of the obtained synthetic quartz powder. Is important to
For this reason, in the oxygen-containing atmosphere, especially in the temperature range of 300 to 600 ° C., which is the desorption temperature of the alkoxy group, it is effective to devise a method of making the temperature rising gradient gentle or providing a hold. is there. On the other hand, when the use of the synthetic quartz powder finally obtained is a quartz glass member used in a high-temperature region of 1000 ° C. or higher, it is preferable that the residual amount of the silanol group after sintering is low because the high-temperature viscosity is high. The residual silanol concentration is preferably 100 ppm or less, more preferably 60 ppm or less. In order to lower the silanol concentration efficiently, the dew point of the atmosphere gas is preferably low, and the dew point is preferably -20 ° C or lower, more preferably -40 ° C or lower. As the maximum firing temperature, the higher the temperature, the higher the diffusion rate of the silanol, so that the target silanol concentration can be obtained in a shorter time.However, sintering of particles, heat resistance of the firing vessel, etc. , Usually 1000
It is carried out in the range of １1300 ° C.

By using the aluminum-containing synthetic quartz powder obtained in this way to melt-mold and form various glass members as quartz glass molded bodies, a transparent quartz glass member can be produced without foaming during melt molding. And a heat resistance higher than that of a conventional synthetic quartz glass member without aluminum addition can be obtained.

Now, the present invention will be described in further detail with reference to Examples. (Example 1) Aluminum acetylacetonate powder:
12.0 g was added to 1000 g of tetramethoxysilane, put in a 1-liter plastic container, and allowed to stand at room temperature for 24 hours in a tightly sealed state (this is referred to as solution A). Next, 5
Into a liter separable flask with a jacket, 2,000 g of tetramethoxysilane and 4 g of solution A left for 24 hours were charged, and 1184 g of water was added with stirring to start a hydrolysis reaction. The jacket temperature during this reaction was 50 ° C. At first, the solution was cloudy in an emulsion state, but became a transparent homogeneous phase after about 20 minutes. After a further 3 minutes, the reaction solution was transferred from the lower part of the reaction container to a 5-liter plastic container and allowed to stand and gel. The gelled product was pulverized while passing through a nylon net having an opening diameter of 900 μm, vacuum dried at 200 ° C. for 10 hours to obtain a dry gel powder, and classified into a range of 100 to 500 μm. When the specific surface area of this dry gel powder was measured by a nitrogen adsorption method, it was 688 m ² / g.
Thereafter, the dry gel powder was placed in a 2 liter square quartz glass container and set in an electric furnace. While flowing dehumidified air with a dew point of -40 ° C over the surface of the charged powder, 500
Temperature in 2 hours, hold at 500 ° C for 10 hours, 120
The temperature was raised to 0 ° C. in 4 hours and baked at 1200 ° C. for 40 hours. No black foreign matter was found in the Al-containing synthetic quartz powder obtained after firing. As a result of the analysis, it was confirmed that the aluminum content in the powder was 4.8 ppm (manufactured so that the target concentration was 5 ppm), and that aluminum was doped substantially as calculated. Further, the obtained calcined powder is fused with an oxyhydrogen flame (Bernui method).
As a result, an ingot having a size of 15 mmφ × 50 mmL was produced, and a colorless and transparent foam-free product was obtained.

Example 2 12.0 g of aluminum acetylacetonate powder was added to tetramethoxysilane: 10
00g, put this in a 1 liter plastic container,
The mixture was allowed to stand at room temperature for 10 hours in a sealed state (this is referred to as solution B). Thereafter, calcination was performed in the same manner as in Example 1 except that the solution B was used in place of the solution A of Example 1, thereby producing an aluminum-containing synthetic quartz powder. No black foreign matter was particularly found in the obtained fired powder. on the other hand,
When the specific surface area of the dry gel powder obtained in the middle stage was measured, it was 515 m ² / g. As a result of the analysis, the aluminum content was 4.8 ppm (target concentration 5 p
pm), and it was confirmed that aluminum was doped substantially as calculated. Further, the calcined powder thus obtained was subjected to a 15 m
When an ingot of mφ × 50 mmL was produced, a colorless and transparent one without bubbles was obtained.

(Comparative Example 1) Aluminum acetylacetonate powder: 12.0 g was added to tetramethoxysilane: 10
To a 1 liter plastic container,
After sealing, it was left at room temperature for 2 hours (this is referred to as solution C). Thereafter, calcination was carried out in the same manner as in Example 1 except that the solution C was used in place of the solution A of Example 1, to produce an aluminum-containing synthetic quartz powder. Observation of the obtained fired powder revealed that black foreign matter was generated at a rate of several particles / about 50 g. On the other hand, when the specific surface area of the dry gel powder obtained in the middle stage was measured, it was 320 m ² / g. As a result of the analysis, the aluminum content was 4.7 p.
pm, and it was confirmed that the doping was performed almost as calculated. Further, when an ingot of 15 mmφ × 50 mmL was prepared from the obtained fired powder by an oxyhydrogen flame melting method (Bernui method), many bubbles of several tens μm to 1 mmφ were confirmed.

[0019]

According to the present invention, there is little foaming during melting,
A good aluminum-containing synthetic quartz glass powder can be obtained.

Claims (4)

[Claims] An aluminum compound is added to a silicon alkoxide, and then water is added to hydrolyze, gel, pulverize, dry, and calcine to produce an aluminum-containing synthetic quartz powder. A method for producing an aluminum-containing synthetic quartz powder, comprising adding a chelating compound of aluminum to a silicon alkoxide, allowing the mixture to stand for 5 hours or more, and then adding water to start a hydrolysis reaction. 2. The method for producing an aluminum-containing synthetic quartz powder according to claim 1, wherein aluminum acetylacetonate is used as the aluminum chelate compound. 3. A silicon alkoxide which is made of aluminum
When the concentration of Al to SiO 2 _Two60-1 on base
After adding 500ppm and leaving it for more than 5 hours
Silicon alkoxide is added to the Al
_TwoHydrolysis by adding water to 1 to 50 ppm in base
The reaction according to claim 1 or 2, wherein the reaction is started.
A method for producing an aluminum-containing synthetic quartz powder. 4. A method for producing an aluminum-containing synthetic quartz glass compact, comprising melt-molding the aluminum-containing synthetic quartz powder obtained by the production method according to claim 1.